The CHALLENGE AER-200 Respirometer System consists of one or more biological reaction vessels, gas flow measuring cells, and a computer. The gas measuring base contains eight flow cells and associated interconnecting circuitry. As gas flows through each cell under the influence of a slight pressure caused by gas production in the reaction vessel, bubbles of a fixed volume are formed in the lower section of the ceil. These bubbles in turn pass through a detection section where a counter is activated. Finally, the number of bubbles is registered by the computer to produce a measure of flow volume and rate. This data is stored by the computer for later data processing.